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In this paper a novel signaling protocol for co-existence and spectrum sharing among cognitive radio nodes is proposed. This protocol allows the radios to rendezvous with each other in a statically allocated spectrum band through on-off keying signaling and reliable spectrum sensing. It enables the radios to have non-cooperative communication in the sense that they do not need to exchange their modulation schemes and frequency channel. The proposed protocol requires no synchronization and is augmented with power control mechanisms. Analysis of the proposed protocol in terms of timing, probability of a successful connection and energy efficiency is also given.

In this paper, a new method is proposed for low complexity localization based on measured/estimated ranges. First, it is proved that the method provides a better estimator than the well known non-iterative direct methods documented in literature, i.e. the Spherical Interpolation and the Linear Least Squares method. It does so by exploiting two similar full constrained models. The proposed estimator is better, in the sense that it corresponds to an equal or smaller value of the original least-squares objective function. Second, the method goes without iterations, and therefore requires considerably less computation power than the iterative techniques such as the Gauss-Newton method. Validation is performed based on actual Ultra-WideBand (UWB) radio measurements conducted in typical office environments, with signal bandwidths varying from 1 to 7.5 GHz. Results show that the position estimates obtained with the proposed non-iterative method have lower root mean squared errors than any other tested well-known direct methods.

In this letter, closed-form expressions for the bit error rate of M-ary pulse amplitude modulated signal constellations as a function of the analog-to-digital converter word length, the signal-to-noise ratio and the fading distribution, are derived. These results allow for a rapid and accurate evaluation of the system performance when the analog-to-digital converter resolution is limited, as is generally the case in high sampling rate communication systems, and thus provide a useful tool for system design, analysis and optimization.

In this paper, a new low-complexity TOA estimation strategy for UWB signals is proposed. It is shown that the TOA of the first peak of the received signal can be obtained with a simple analog receiver implementation which requires sampling rates in the order of only a few tens of MHz; at the same time, the achieved range error standard deviation is at centimeter level. A link budget evaluation under the power requirements imposed by the FCC shows that, with the suggested set of system parameters, maximum coverage of this solution is of a few hundreds of meters in LOS, making this approach ideal for low-cost, short to medium range systems which require centimeter positioning accuracy.

Recently radio frequency (RF) level antenna diversity combining has been proposed as a low cost and power efficient alternative to conventional antenna diversity combining. In RF level diversity combining the diversity weights are implemented in the hardware by making use of circuit elements such as phase shifters and variable gain amplifiers, while channel estimation is performed in the digital baseband domain. In this paper, we analyze the performance of an RF level equal gain combiner. Two alternative but numerically equivalent representations of the probability density function and characteristic function of the combined signal amplitude for binary phase shift keying signals (BPSK) over Rayleigh fading channels are derived. The newly derived characteristic function is then used to evaluate the error probability. Finally, we compare the performance with binary frequency shift keying (BFSK) and differential binary phase shift keying (DBPSK) schemes with diversity reception. It is shown that for only 3 level phase compensation, BPSK exhibits superior performance to both BFSK and DBPSK.

A statistical model for the range error provided by TOA estimation using UWB signals is given, based on UWB channel measurements between 3.1 and 10.6 GHz. The range error has been modeled as a Gaussian random variable for LOS and as a combination of a Gaussian and an exponential random variable for NLOS. The distance and bandwidth dependency of both the mean and the standard deviation of the range error has been analyzed, and insight is given in the different phenomena which affect the estimation accuracy. A possible application of the model to weighted least squares positioning is finally investigated. Noticeable improvements compared to the traditional least squares method have been obtained.

In this paper, a low complexity way to improve the Linear Least-Squares (LLS) method is introduced. The n-dimensional (n-D) positioning problem is first reduced to 1-D and then solved iteratively. Compared to the classic Gauss-Newton method, the n×n matrix inversion/factorization in each iteration is reduced to the inversion of a scalar. Simulations are performed to compare the Gauss-Newton, the LLS and the improved LLS method versus the Cramer-Rao Lower Bound (CRLB). The Mean Squared Error (MSE) of the obtained estimator is very close to that of the Gauss-Newton method, while the computational complexity is kept at almost the same level of the LLS approach.

In this paper, a statistical model for the range error provided by TOA estimation using UWB signals is given. To this purpose, a large set of UWB channel measurements covering the bandwidth between 3.1 and 10.6 GHz has been collected and processed. By analyzing the measurement results, the range error has been modeled as a Gaussian random variable for LOS and as a combination of a Gaussian and an exponential random variable for NLOS propagation. The distance and bandwidth dependency of both the mean and the standard deviation of the range error has been investigated, and an insight in the different phenomena which affect the estimation accuracy, is provided. It is shown that both the signal bandwidth and the distance between the transmitter and the receiver, significantly affect the range error characterization. From the proposed model, the estimation accuracy achieved by TOA-based UWB ranging on the global set of measurements has been derived and compared with the data. For LOS, using the full bandwidth, the range error is at centimeter level; it increases in NLOS due to the additional delay introduced by the propagation through dielectric materials and to the more dense multipath.

Noisy radio frequency (RF) circuits tend to degrade the system performance, especially in high frequency communication systems. The performance analysis of such systems is normally based on Monte Carlo simulations which are rather time consuming and provide little insight for system performance bottle necks. In this paper, an exact closed form expression for the bit error rate (BER) of M-ary pulse amplitude modulated (MPAM) single carrier (SC) schemes as a function of analog to digital converter (ADC) word length is presented. This expression is then used for the performance evaluation of MPAM schemes perturbed by Gaussian and ADC quantization noise (QN) in various fading scenarios. The expressions presented can also be used to determine the system performance in the presence of other RF imperfections such as phase noise in addition to ADC noise and thus provide the system designer with a handy tool for RF system design and optimization.

Ultrawideband (UWB) technology is an attractive alternative for short-range applications, e.g., wireless personal area networks. In these applications, transmit and receive antennas are very close to each other and the far-field condition assumed in most of the link budget models may not be satisfied. Under near-field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this work, a novel line-of-sight UWB link budget model for very short distances is proposed and validated with measurements using different types of antennas. The proposed model, which takes into account all main near-field effects (i.e., phase error, antenna mismatch and reradiation between antennas) and includes frequency, antenna size and orientation as parameters, shows a good agreement with the simulations and the measurements. This model has also been applied to dispersive antennas (e.g., notch-antennas), and can be used in the design and analysis of short-range UWB communication systems.

Sharing of the frequency spectrum between licensed primary users and unlicensed secondary users (SUs) requires reliable detection of spectrum occupancy by the SUs. Due to fading, single terminal detection is unreliable and results in a high probability of missed detection. This problem is solved by applying cooperative detection. In this paper two novel energy-based cooperative detection methods using weighted combining for Dynamic Spectrum Access are presented and analyzed. Weighting is based on the local mean SNR and the optimum log-likelihood ratio. Simulation results show a substantial improvement for the proposed weighting methods compared to equal gain combining and hard decision combining.

This paper addresses the non-linearity effect when using iterative least-squares (ILS) methods for indoor positioning, where coordinates are to be determined based on estimated/measured ranges. Dealing with non-linear inverse problems, the obtained least-squares estimator is inherently biased and the bias is usually negligible in satellite positioning systems, e.g. GPS, or other large scale systems. However, in indoor systems, the bias can be significant and therefore extra care needs to be taken to properly apply the ILS methods. Special attention is given to the Gauss-Newton method, since it is well suited for solving (small residual) non-linear problems [1] and most commonly applied in positioning. A scheme to test the significance of the bias due to non-linearity is proposed. The validation of the proposed scheme is experimentally supported by an UWB acoustic positioning demonstrator. By scaling the frequencies with a specific factor (the speed of light over the speed of sound), it is possible to observe similar interactions with the environment using audio signals as for radio UWB signals. This well-affordable acoustic UWB positioning demonstrator can be used to investigate the capabilities of UWB radio signals for potential indoor ranging and positioning applications. The non- linearity effect is analyzed with a number of system setups, differing in the positions of transmitters, the position of the receiver, redundancy, the bandwidth used and therefore the range measurement error. Preliminary results show that centimeter level positioning accuracy can be reached using the audio band between 3.6 and 12.1 kHz (corresponding to the full band between 3.1 to 10.6 GHz allowed for UWB radio communications).

Circuit technology for 60 GHz is still limited, and impairments due to radio frequency (RF) circuit imperfections must be taken into account. Therefore, the candidate transmission schemes, in addition to multi-path fading, should be fairly resistant to RF circuit imperfections. In this paper, a performance comparison of multi-carrier (MC) and single-carrier (SC) based transmission schemes in the presence of DAC/ADC imperfections and amplifier nonlinearities, is carried out. It is shown that the SC scheme has substantially lower front-end requirements than its MC counterpart, while having the same overall system complexity.

This paper addresses the feasibility of using iterative least-squares (ILS) methods for indoor positioning, where coordinates are to be determined based on estimated/measured ranges. Special attention is given to the Gauss-Newton method, since it is well suited for solving (small residual) non-linear problems and most commonly applied in positioning. Dealing with non-linear inverse problems, the parameter estimation possibly features local minima next to the sought for global one, and the position estimator is inherently biased. In satellite positioning systems, e.g. GPS, or other large scale systems, an initial guess that leads the iterative method to a global convergence is not hard to obtain, and the bias due to non-linearity is negligible. However, in indoor systems, both effects can become problematic, and therefore extra care needs to be taken to properly apply the ILS methods. Two schemes are proposed in this paper, one to obtain a good initial guess and the other to test the significance of the bias due to non-linearity. The validation of the proposed schemes is supported by simulations as well as by experimental results obtained with an UWB acoustic positioning system, which achieves centimeter level positioning accuracy with LoS propagation and full bandwidth between 3.6 and 12.1 kHz (with equal wavelength compared to the radio signals with the bandwidth between 3.1 to 10.6 GHz allowed for UWB radio communications). The proposed schemes are validated with a number of system setups, differing in the positions of transmitters, the position of the receiver, redundancy, the bandwidth used and therefore the range measurement error.

Wireless personal area networks applications may benefit from the use of ultra-wideband (UWB) technology. In these applications transmit and receive antennas are very close to each other and the far-field condition assumed in most of the link budget models may not be satisfied. Under near- field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this work, a new UWB link budget model for very short distances is proposed and validated with measurements using different types of antennas. The measurements have been performed in the time domain by exciting the antenna with very short pulse of 35 ps width covering a large frequency band. The proposed model, which includes frequency, antenna size and orientation as parameters, shows a good agreement with the simulations and the measurements.

The 60 GHz band, with a large unlicensed bandwidth, is an excellent choice for short distance high-speed communications. However, radio frequency (RF) circuit limitations at 60 GHz give rise to impairments such as phase noise, in-phase/quadrature-phase (I/Q) imbalance and amplifier nonlinearities. The candidate transmission schemes, in addition to multi-path fading, should therefore be fairly robust against RF circuit imperfections. This paper investigates the performance degradation as a function of various circuit parameters for multi-carrier (MC) and single-carrier (SC) schemes, which can be useful for:( i) performing a system cost and performance tradeoff comparison, (ii) identifying main performance bottle necks for MC and SC based systems.

UWB technology has been recognized as an ideal candidate to provide positioning information in indoor environments. However, demonstrators useful to test UWB positioning algorithms are still difficult to realize due to the hardware requirements of this technology and the scarceness of components available in the market. For this reason, the use of an acoustic demonstrator is proposed. By scaling the frequencies with a specific factor, it is possible to obtain the same wavelengths for the audio signals as for the radio signals. In this way, similar interactions with the environment can be observed. A validation of this technique is provided, by analyzing and comparing the large scale statistics and the RMS delay spread of the channel impulse response obtained with the two types of signals, and the similarities and differences are underlined. Finally, first results on the TOA estimation accuracy for different propagation conditions and on the positioning performance achievable using audio signals are shown. With the proposed audio demonstrator an accuracy at centimeter level can be achieved for LOS propagation.

This paper explores the possibility to design an indoor ultra wideband (UWB) ranging and positioning system using the received signal strength (RSS). Due to the extremely large bandwidths, the effects of small scale fading are reduced to the level where the knowledge of the path loss model (PLM) can be employed for accurate and reliable distance estimation. This approach enables trilateration based position estimation while significantly reducing the synchronization effort. A limited number of measurements is necessary in order to calibrate the PLM parameters but no extensive database of measurements is required, such as in fingerprinting methods. Based on simulated UWB channels, the effects of uncertainties in the PLM parameters on the estimated distance are characterized. Data from a UWB measurement campaign in indoor line-of-sight (LOS) scenarios are used to verify the performance of such a system.

In this paper, the results of ultra wide band (UWB) measurements carried out in indoor environments are presented and a statistical propagation model for the UWB channel covering the frequency band from 3.1 to 10.6 GHz is proposed. The measurements have been performed in the time domain by exciting the channel with very short pulses of 50 ps width. Both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation with a maximum distance of 10 m are considered. Inspection of measured data after processing shows that the multipath components of the UWB channel tend to arrive in clusters. Therefore, the Saleh-Valenzeula (S-V) model has been adopted as starting point for our modelling analysis. Important channel parameter statistics of the model are extracted from the measured data. The obtained results show some discrepancies with respect to the IEEE channel model. The results presented here illustrate that the conventional single Poisson process is not sufficient to model the cluster and ray arrival times. Therefore, a Gamma distribution is proposed to model the cluster inter-arrival times and a mixture of two Poisson processes to model the ray intra-arrival times. It is found that the amplitude fading statistics can be modelled by the log-normal distribution with a standard deviation decreasing linearly with the excess delay. Other parameters like cluster and ray power decay constants are determined to complete the statistical UWB channel model.

In this paper we give insight into the performance of Dynamic Spectrum Access Networks (DSAN), analyzing Quality of Detection of Primary User (PU) and DSAN blocking probability, when the channel is under the effect of log-normal shadowing. Specifically we propose a distributed power conserving PU detection architecture and investigate the impact of PU detection accuracy on DSAN performance. We measure DSAN blocking probability as a function of the number of PU channels and their utilization. Finally we propose two efficient DSAN channel access schemes called Least-used and Least-used with Channel Hopping which aim at minimizing packet dropping due to the arrival of the PU.

Rotation of the signal constellation together with in-phase and quadrature channel interleaving (signal space diversity) is known to provide good performance gains over fading channels for multi level modulation methods. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and un-coded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional un-rotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the un-coded scheme.

Ultra wide band (UWB) technology is prone to be used in wireless personal area networks (WPAN) applications. In these applications transmit and receive antennas are very close to each other and the far field condition assumed in most of the link budget models may not be satisfied. Under near field conditions, variations in the link budget and pulse shape with respect to the far field can be observed. In this work, near field WPAN measurements have been carried out with three different bi-conical antennas in order to analyze the link budget. A new link budget model is proposed and compared with the measurements. Results can be used in the design and coverage analysis of UWB communication systems for WPAN applications

This paper presents the results of ultra wide band (UWB) channel measurements for wireless personal area networks (WPAN). A time domain measurement setup has been developed covering the frequency band from 3.1 GHz to 10.6 GHz. Relevant scenarios for WPAN applications have been proposed and measurements have been conducted in an office at very short distances including both LOS and NLOS cases. Additional NLOS measurements with a human body obstructing the direct path have also been performed to determine the effects of the body on the UWB-WPAN channel characteristics. In addition to this, the near field effect between transmit and receive antenna has been examined and channel parameters such as root-mean-square (RMS) delay spread, Ricean K-factor and path-loss exponent are obtained. These results can be used for analysis and design of UWB systems for WPAN applications

The performance of uncoded phase-shift-keying (PSK) and quadrature amplitude modulation (QAM) schemes over fading channels can be improved by using coded modulation techniques. Improvement is due to the coding gain coupled with interleaving and depends on the complexity of the code. Recently, it was shown that constellation rotation coupled with interleaving can be used to improve the performance of QPSK modulation over block-fading single-input-single-output (SISO) wireless communication channels. This paper considers the use of such a scheme with higher order constellation sets such as 8PSK and 16QAM. A framework is then presented for the calculation of the optimum rotation angle for MPSK/MQAM schemes. A simple cost function based on the union bound of the symbol error probability (SEP) is defined. The optimum rotation angle is then found by minimizing the cost function using the gradient search algorithm. The obtained simulation results show considerable improvement over the conventional unrotated system.

In this paper, ranging based on UWB signals is investigated for indoor dense multipath environments. To this end, a large set of time domain measurements covering the 3.1-10.6 GHz frequency band is carried out. Different approaches to detect the time of arrival of the first path are evaluated. Ranging results based on time estimation are compared to those based on signal strength. Additionally, the effect of the bandwidth on the range estimates is analyzed. Generally, the results show that high ranging accuracy can be achieved for both LOS and NLOS propagation when UWB is used. Analysis of the data points out that additional delay introduced by propagation through walls is the main source of range error in NLOS indoor environments.

A power efficient embedded QAM (EQAM) modulation scheme, for addressing multiple users simultaneously in the downlink of a cellular system, is proposed. The EQAM modulation is based on stacking a number of M-PSK (M = 2,4) signals each intended for a different user. The optimum phase relations between the users' signals and the required link quality dependent amplitudes, are given. The power penalty is evaluated for geometrically related link qualities and for a number of heuristic user assignment schemes in a single cell system. Compared to a conventional QAM-scheme with the same spectral efficiency, the power penalty for EQAM can be substantially lower, provided that users with sufficiently different link qualities are addressed with the same signal.

This paper evaluates the performance of a dual-signal receiver (DSR) when used for short-range communications on a motorway. Vehicles send small packets with equal transmitting power to a base station near the motorway using the slotted Aloha protocol. The positions of the vehicles are derived from real vehicle measurements. The measurements are split into three traffic conditions: queuing traffic with low vehicle speeds, heavy traffic with small average headway's, and light traffic. A DSR is used, and compared with a capture receiver. Success probabilities are calculated using a free space power loss model and Rice distribution. The success probabilities are used to analyse the throughput and delay characteristics for the slotted Aloha protocol in the uplink data stream, under different traffic conditions. The results show that the DSR benefits from the near-far effect. The total throughput for all vehicles is significantly higher than for the capture receiver.

The performance of a conventional threshold detector for a frame differential autocorrelation receiver in IR UWB systems in a dense multipath channel are improved by means of appropriate chip code and delay hopping code design. We point out which conditions must be satisfied by the delay hopping code in order to reduce the nonlinear ISI and the bias term, which are peculiar nuisance parameters of autocorrelation receivers. Moreover, by extending the periodicity of the chip code, we show how to suppress linear ISI. Simulated results confirm the performance improvement in terms of BER. An analytical expression relating the noise power to the system parameters is also presented. These results can be extended to the well known transmitted reference systems.

The interframe (IFI) and intersymbol interference (ISI) of a symbol-differential autocorrelation receiver (SD-ACR) for an impulse radio ultra wideband (IR UWB) system in a multipath channel is evaluated. The system can be modelled as a nonlinear filter with respect to the input data sequence. The filter's coefficients are random variables for which we derive an accurate statistical description up to the second moments. The analysis shows the presence of a bias term, that makes the optimum decision threshold different from zero. The results obtained in this paper provide a good understanding of the performance degradation due to ISI and IFI and they show the impact on system design. Analytical results, confirmed by simulations point out a new concept for the pulse positioning within the symbol interval, and the transmission of one pulse per symbol emerges as the optimum choice for the single user case. Simulated results for the noise-free ideal environment confirm the influence of the system parameters in terms of BER and provide a measure of the achievable bit rate as a function of the channel RMS delay spread.

In this paper we address the problem of radio resource allocation for QoS support in the downlink of a cellular OFDMA system. The major impairments considered are cochannel interference (CCI) and frequency selective fading. The allocation problem involves assignment of base stations and subcarriers, bit loading, and power control, for multiple users. We propose a three-stage, low-complexity, heuristic algorithm to distribute radio resources among multiple users according to their individual QoS requirements, while at the same time maintaining the QoS of already established links in all the cochannel cells. The allocation objective is to minimize the total transmit power, which adds to reducing CCI. Simulation results show a superior performance of the proposed method when compared to classical radio resource management techniques. Our scheme allows us to achieve almost 6 times higher capacity (sum data rate) than the method based on FDMA with power control, at a blocking probability of 0.02.

In this paper we propose two innovative detection schemes for IR-UWB communication systems based on the autocorrelation receiver and differential detection. The proposed schemes avoid the need for a complex analog multiplier by employing: (i) a limiter in the reference branch only; or (ii) employing also a limiter in the signal branch. Analytical models for the statistics of the decision variables are presented for the receivers, and the analytical and simulated BER exhibit an excellent agreement. We point out the dependence of the performance on some important system parameters, that shows the system design trade-off between receiver complexity and performance.

We consider the problem of radio resource allocation for QoS support in the downlink of a cellular OFDMA system. The major impairments present are co-channel interference (CCI) and frequency selective fading. The allocation problem involves assignment of base stations, subcarriers and bits, as well as power control, for multiple users. We evaluate the performance of a three-stage, low-complexity, heuristic algorithm, which allows to distribute radio resources among multiple users according to theirs individual QoS requirements, while at the same time maintaining the QoS of already established links in all co-channel cells. The evaluation includes checking system operation for various conditions described by different: a) delay spread, b) data rate required by a single user and c) path loss. It is shown that the proposed method is superior in terms of offered traffic and blocking probability to classical method based on FDMA with power control. Also, the performance of our scheme increases in highly frequency selective environment, disastrous for classical fixed schemes, since our method benefits from multiuser diversity.

This paper proposes a soft-iterative multiuser receiver of low complexity, based on the principle of turbo decoding. A serially concatenated system is used, where every user employs a convolutional code, interleaver, space-time block code (STBC) and the spreading operation. The proposed receiver uses a soft-input soft-output (SISO) multiuser detector-decoder, which is basically a soft interference canceller for the space-time coded wideband code division multiple access (WCDMA) signal. In each iteration, extrinsic information is interchanged between the different SISO blocks giving asymptotically unbiased estimates. The introduction of STBC adds decorrelation between the different user signals, relaxing the interleaver design and less iterations are needed for the system to converge. The receiver allows the use of a less complex soft matched filter instead of a minimum mean square error (MMSE) filter. It achieves nearly single-user performance, and gives an excellent trade-off between implementation complexity and performance for advanced WCDMA multiuser receivers.

With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same channel without using a bandwidth expanding signature code when sufficient power differences at the receiver are maintained. In this paper, we estimate the capacity that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on successive cancellation. The power control algorithm is adapted to multiple users per channel in a cell. Capacity results from simulations based on user removal are presented for three removal algorithms. It is shown that the narrowband MUD has a significant potential for capacity gain due to a tighter packing of users in a channel.

In this paper we consider the problem of resource (subcarrier and transmit power) allocation for QoS (quality of service) support in OFDMA systems with fixed modulation per subcarrier. We identify the key QoS parameters, such as bit rate and bit error rate, which are then used to determine the individual users' traffic demands. We propose an extension of Wong's (1999) algorithm, which distributes subcarriers and transmit power among multiple users according to their QoS traffic requirements. The new scheme, available in optimal and suboptimal version, is less complex than most of the existing methods. Due to its orientation on individual traffic requirements, it does not waste resources in a worst-case design. This results in a better performance compared to the Wong's algorithm. Moreover, we fit the considered resource allocation algorithm into a general contract-based QoS/CoS (cost of service) framework, which allows for efficient management of resources on the system level.

A carrier recovery loop based upon decision-directed IF remodulation techniques is presented. The 16-QAM signal is converted into a 3-ary ASK signal containing a discrete carrier component, which can be tracked by a phase-locked loop. The symbol timing recovery is accomplished by a coherent early-late tracking loop, which uses decision feedback as well. Thus, the carrier recovery, the symbol timing recovery, and the data detection are strongly interrelated processes, each being of vital importance for the correct demodulation of the received 16-QAM signal. >

Propagation measurements were performed in an indoor radio environment at 2.4 GHz, 4.75 GHz, and 11.5 GHz using a coherent measurement system consisting of an HP synthesized sweeper and a network analyzer. The three frequencies are compared by evaluating the RMS time delay spread and path loss characteristics. Such frequency comparisons in an indoor radio environment are reported. >

The paper analyses the performance of quasi-coherent combining of signals from a small circular antenna array in a Rician fading indoor multipath channel at microwave or millimetre wave frequencies. Instead of maximum ratio combining, where the complex weighting of signals results in an optimum for a single frequency, the proposed concept is based on quasi-coherent combining of the dominant component of the multipath signal of each antenna. The resulting channel impulse response, shows less delay spread and a higher signal to noise ratio. A scheme for this combining technique is given for a coherent binary phase shift keying receiver and evaluated by simulation. Cumulative BER results for the Rician channel and normalised bit rates are presented for circular arrays of 1, 2 and 4 antennae with a diameter of one wavelength. It is shown that this combining technique results in a significant improvement of the BER or application of higher bit rates,.

An analytical model for bit error rate (BER) evaluation of the time invariant frequency selective indoor channel is developed for a coherent binary phase shift keying receiver. BER performance for the millimetre wave channel is computed, based on impulse response models derived from measurements. The performance appears to be predictable, depending on the power-delay-profile type and the Rice K-factor of the channel. Multiple antenna performance is analysed and compared for antenna selection diversity and multiple antenna signal combining. It is shown that signal combining results in substantial performance improvement, whereas selection diversity appears to be less promising.

The paper analyses the performance of a dual-signal receiver in a Rician fading channel. The receiver is designed for simultaneous reception of two narrowband binary phase shift keying (BPSK) modulated co-channel signals, e.g. two desired signals, of different strength. The dual signal receiver consists of two demodulators. The principle of operation is based on separation of both signals using the data signal of the large signal which is estimated by the first demodulator. After cancellation of the large signal, the small signal is demodulated. The bit error rate (BER) and receiver outage performance in the Rician fading channel with additive white gaussian noise are derived for both signals. Numerical results are presented for two receiver structures with different second demodulator: (i) the coherent BPSK demodulator; (ii) the differentially coherent (DPSK) demodulator. It is shown that the dual-signal receiver outperforms the conventional receiver significantly, especially in the interference limited channel with high signal-to-noise ratio.

A measurement system for determination of the characteristics of radio paths in a multipath channel is discussed, and measurement results are presented. The measurement system uses direct-sequence spread-spectrum modulation and operates in the VHF band (30-70 MHz). A carrier, BPSK modulated with a pseudo-noise (PN) sequence at a rate of 1 Mchip/s, is used to sound the radio channel. From the coherently received in-phase and quadrature-phase signals the characteristics of the different radio paths-relative amplitude, RF-phase, and delay-time-are calculated. The accuracy of the measurement system has been determined, and is 2 dB for amplitude information, 5 degrees for the RF-phase, and 20 ns for the delay-time. >

The dual-signal receiver (DSR) for simultaneous reception of two co-channel signals, shows large performance degradation for SIR/spl cong/0 dB. In this paper, antenna diversity techniques are investigated to overcome this problem. Computational results for BPSK modulated signals in narrowband and wideband fading multipath channels, show that antenna combining results in a significant performance enhancement for the DSR; the largest improvement is achieved by minimum mean square error combining (MMSEC). For the narrowband Rayleigh fading channel and a four element array, MMSEC performance with two signals is nearly equal to the one signal case for SIR=0 dB. In the wideband channel, the SIR required to achieve good performance, increases with increasing symbol rate due to intersymbol-interference.

The dual-signal receiver (DSR), proposed for simultaneous reception of two narrowband modulated co-channel signals, shows large performance degradation when both signals have about equal strength. The performance enhancement of the DSR using binary phase shift keying (BPSK) modulation is obtained with forward error correction (FEC) coding. Rather short linear block codes were evaluated using hard and soft decision decoding techniques. With soft decision decoding, large coding gains are obtained in the channel with co-channel interference and additive white Gaussian noise (AWGN). The gain for the channel with interference is larger than for the AWGN-channel, but the absolute performance is worse. Hard decision decoding gives no significant enhancement. The coding gain for the small signal is about the same as for the large signal due to the occurrence of correlated errors.

A narrowband multiuser receiver based on successive signal detection and subtraction is proposed. The symbol error probability (SEP) for M-PSK modulated signals is evaluated and analytical approximations for the SEP of the individual signals are presented and compared to results obtained from simulations. The effect of inaccurately estimated signal parameters due to noise is analyzed. The SEP results are presented for synchronous signals for the additive white Gaussian noise (AWGN) channel. For geometrically related amplitudes the minimum required amplitude ratio is shown to be dependent on the modulation level M and the number of cochannel signals.

The previously developed subspace techniques for estimation of parameters and recovery of WCDMA signals embedded in frequency selective channels have been probed as a very promising techniques with great theoretical and practical importance. Particularly, this paper extends a blind channel estimation algorithm based on intersection of subspaces. Such a scheme is used together with a JADE ESPRIT algorithm, which calculates jointly the relative delays and AOAs of multipath signals based on the shift invariance properties of WCDMA signals. Afterwards, a less complex linear space-time decorrelator with a sliding window of 3 bits over a frequency selective Rayleigh fading channel is studied. We investigate the BER performance of the system by Monte Carlo simulations.

We analyze the error probability of joint detection based on maximum likelihood estimation for simultaneous reception of two narrowband co-channel users. The main contribution herein is to present an exact derivation of the error probability as well as an union bound. Performance results are presented for a Rayleigh fading channel considering multiple antennas. It is shown that, for joint detection using antenna diversity, the performance degradation for both signals is negligible compared to the interference-free case, thus doubling the system capacity.

Multipath fading and multiple access interference (MAI) are the major constraints on the performance of DS/CDMA systems. Antenna arrays and multiuser detectors have been considered to increase the system capacity through mitigation of such impairments. Multiuser detectors have the capability of eliminating MAI, the near-far problem and providing a significant capacity increase. In order to gain from the enhancements of both: multi-user detection and adaptive antenna, we propose in this paper to combine both schemes for an asynchronous WCDMA system. The performance of the combined scheme is evaluated for the uplink over the Gaussian channel and the UMTS frequency selective Rayleigh fading channel. We make a comparison of the most promising multiuser structures and the recursive least square algorithm to control the beamformer.

This paper presents the results of wideband channel measurements and characterization at 17 GHz. Important channel parameters, namely root-mean-square delay spread, Ricean K-factor, propagation loss factor and their statistics are investigated. The measurements were performed for different types of scenarios and for both indoor and outdoor environments. All channel parameters were derived from the power transfer function solely. The path loss factor is found to be lower than the free space attenuation for all LOS sites. The mean value of the Ricean K-factor is 1.5 dB and -1.1 dB for LOS and OBS indoor sites, respectively. For the outdoor environment 4.9 dB was found. The RMS delay spread was found to be about 20 ns for indoor sites, whereas for outdoor sites the average value was two times higher.

In this work we analyse the performance of a simplified single-cell wireless mobile system based on the dual-signal receiver. The dual-signal receiver is a multi-user TDMA receiver which allows the transmission of two signal over the same physical channel. The results are presented as a function of a quality of service. Exploiting only the characteristics of the wireless channel we show that the dual-signal receiver allows a large capacity increase when compared to a conventional GSM-like system.

In order to increase the capacity of WCDMA systems in the uplink while avoiding complexity, we investigate a space-time configuration by employing jointly beamforming and multishot multiuser separation. Such a joint structure provides a better bit error rate performance than either techniques used separately. Specifically, we propose a less complex space-time configuration, which is robust to multiple access interference (MAI) over a frequency selective Rayleigh fading channel. We investigate the BER performance of the system by Monte Carlo simulations. The results obtained show that applying space-time processing using a simple beamforming and multishot separator can improve the performance of WCDMA systems considerably.